What is Capillary Action?
Capillary action is a principle which explains why fluids are often drawn up into other substances. This phenomenon is also sometimes described as “capillarity.” A classic example of capillary action involves a paper towel and a spilled puddle of water: when the towel is dipped into the water, it sucks the water up. Capillarity explains a large number of events which occur in nature, from how trees manage to get water all the way up to their crowns to the way in which water seems to climb up a straw. Several factors are involved in capillary action. The first is cohesion, the tendency of molecules of a substance to stick together. Water is a cohesive element, with a level of cohesion which creates a high degree of surface tension. When water is spilled on a table, it tends to stick together in a puddle, rather than spreading out, because it is cohesive. The second factor is adhesion, the tendency of some substances to be drawn to unlike substances. In the example of a tree and the wate
Capillary action is a physical effect caused by the interactions of a liquid with the walls of a thin tube. The capillary effect is a function of the ability of the liquid to wet a particular material. The liquid for which this effect is most commonly seen is water, because water is capable of strong surface interactions and because water is ubiquitous. Water climbs up a thin glass tube because of the strong hydrogen-bonding interactions between the water and the oxygens (and terminal hydrogens) at the surface of the glass (SiO2; surface oxygens are typically bonded to hydrogen). The energetic gain from the new intermolecular interactions must be balanced against gravity, which attempts to pull the liquid back down. Therefore, the narrower the tube, the higher the liquid will climb, because a narrow column of liquid weighs less than a thick one. One gets the same effect for pores and narrow spaces in any hydrophilic object. While I have not been able to find any information on the Web,
